I was planning to construct a coffee table out of Huon pine, a timber which is now very scarce and expensive. This creamy yellow wood is generally recovered (rather than felled) from areas of Tasmania such as the Teepookana State Forest near Strahan (now a World Heritage area). I couldn’t afford to make any mistakes and was discussing the difficulties that accurate mortise and tenon joinery presented to the amateur woodworker with a professional furniture maker friend. He retorted, ‘Why bother, we hardly ever use them in the shop, we dowel—it’s strong, quick and accurate’. When I scoffed at this he promised to prove it.
I was amazed at just how simple and accurate the process turned out to be. Simply cut the rails square to length, mark out, drill and dowel for perfect flush fitting joints. The secret was a horizontal borer with a table parallel to the drill bit and, importantly, the accurate marking of hole centres.
My friend used a tenon marking gauge (two pins) to simultaneously mark two horizontal lines, indexing from the top of the table legs and top of the rail-ends (photo 1)...
...and a single pin marking gauge for a
vertical intersecting line, indexing from the outside face of the legs and rails (photo 2).
This ensured accurate hole placement indexed to the outsides of the workpiece ends or faces. The components were then placed on a horizontal feed table and drilled with a 10mm dowelling centre bit. This amazingly simple system resulted in perfectly placed parallel holes.
I just had to have one of these horizontal borers and immediately started plotting how to build a home shop version. With accurate positioning solved, the key to successful drilling of the holes was to be able to feed the workpiece square to the drill dowelling bit. I figured that a drill base with a square fence and vertically adjustable feed table wouldn’t be too hard to make—the difficulty would be to mount the drill horizontal to the base and square to the fence. None of the workbench drill holders that I could purchase were sufficiently robust. I was on the point of making a wooden cradle and collar when I happened upon a handyman extruded aluminium bench top lathe bed for portable drills. Pretty useless (I suspect) for its intended purpose, but perfect for mine.
I cut 260mm from the lathe bed and mounted it centrally on a line scribed down the middle of a 540 x 220 x 25mm MDF base. This provides a strong and accurate mounting for my old power drill (which never thought it would see duty again!). It can also be adjusted fore and aft to set the drilling depth.
The stop fence is another MDF scrap (18mm) with a groove routed vertically down its centre. The drill piece protrudes through it from one side and the feed table’s hardwood tongue can slide up and down it from the opposite side (photo 3). The tongue contributes to table stability when adjusting height.
Feed Table Adjustment
It was important to be able to adjust the feed table in very small increments and lock it square to the fence. I achieved this by gluing a hardwood return lip to the front edge of the table. After adjusting the table for height I clamp the lip to the fence (photo 4).
The height adjustment mechanism is made of one inch threaded rod with two steel nuts (to minimise slop) welded to a mounting plate. The threaded rod is fed through the mounting plate from underneath the unit’s base (main photo). A third nut with a lever locks the table height. The lathe bed came with a cast aluminium face plate which I bored to sit on top of the threaded height adjustment rod. The MDF feed table sits on top of this.
I grooved the table for mitre gauge tracks to ensure accurate drilling of both end and side pieces. The gauge feeds the workpiece square to the drill bit and protects fingers. It’s the kind that comes with benchtop grinding and sanding tools.
On finishing the dowelling jig I was immediately inspired to construct a matching end table. Set up time was only minutes and the results were perfect (photos 5 and 6). A trial run to check accuracy is an option, rather than a necessity.
The wood cost nothing (all scraps), the threaded rod and nuts less than $15 (a friend did the welding), and the lathe bed $45. Design and construction took a weekend. Not bad value for a device that will join four corners of a construction (eight joints) dead accurate, square and flush in minutes. With hours of mortise and tenoning time saved!
I think I enjoyed building the drilling jig even more than I do using it—because it took two days to design and build, and only takes minutes to use.